Constitutive equations for time independent plasticity and creep of 316 stainless steel at 550°C

Abstract

The paper concerns the development of constitutive equations for 316 stainless steel at 550 8C; it, firstly, considers time independent plastic straining at high temperature; and, secondly, describes how mechanisms-based creep constitutive equations have been formulated. It is shown how a power-law hardening model may be used to describe the effects of prior plastic pre-strain, by providing excellent comparisons with the results of experiments. The paper then develops constitutive equations for time dependent creep based on the theory of continuum damage mechanics. The corresponding state variable rate equations have been selected to include a description of strain hardening in primary creep, a major contributor to strain in this material, and also softening due to creep constrained cavity growth. Despite the paucity of data at lower stresses, corresponding to lifetimes in the region of 10 5 h, a model has been formulated which gives good predictions of experimental results over a wide stress range. The paper discusses how the time independent and time dependent models may be combined in a finite element analysis code to predict inelastic straining due to initial loading and to stress redistribution encountered in reheat cracking of welded pressure vessels. q

The influence of test duration and geometry on the creep crack initiation and growth behaviour of 316H steel

“…A tail of this shape may be related to primary creep effects whilst damage builds up at the crack tip. Primary creep has been found to be more pronounced for this material and temperature at low stresses [10], which may explain why tests at relatively low load on the low constraint DEN(T) specimen, with therefore relatively low crack tip stress values, show significantly longer tails than the other tests in Figure 2.…”

Finite element analysis of elastoplastic modeling: application to one-dimensional loading of as-received and pre-strained materials

“…Some experimental results obtained from uniaxial test on 316 stainless steel at 550 • C are used here to obtain the values of k and m equal to 560 MPa and 0.3045, respectively, for this material. The value of Young's modulus is reported equal to 122,630 MPa [15]. It is seen in Fig.…”

“…6). 3.2 FEA for pre-strained material Hayhurst et al [15] have considered that parameters of constitutive equation become different when the material under consideration is changed from as-received material to the pre-strained one. However, as seen in the mathematical treatment of the model presented in this work, the same constitutive modeling with the same parameters is considered for both materials.…”

“…Hayhurst et al [15] have also studied the behavior of 316 stainless steel with a pre-strain of 0.05. To simulate the uniaxial behavior of pre-strained material, it is sufficient to introduce the initial value of equivalent plastic strain into the analysis.…”

“…This could be an encouragement to use the proposed model in finite element analysis of multidimensional loading paths. However, as can be noticed, some particular phenomena observed in the behavior of pre-strained material [15] such as variation of Young's modulus depending on pre-strain value or anisotropy induced by pre-strain [4,5] are not taken into consideration by this modeling.…”